Round Numbers and An Approaching Milestone

People love round numbers; baseball people love them especially.  As such, this post is about one particular round number.

There is a lot to like about the website Baseball Reference. One oft-overlooked feature though, in my opinion, is the information provided for each player’s debut.  As part of each MLB player’s general bio, Baseball Reference provides information on when and where their debut was, what they happened to do on that unique day, and additionally mark that individuals “place in line” upon arriving in the Major Leagues.  For instance, Justin Turner, according to baseball reference’s bio information, was “17,262nd in MLB history” to make his MLB debut.

For those who pay attention to this particular facet of Baseball Reference’s player bios, it might have already been considered that the number of players who have appeared in at least one MLB game is approaching a very round number: 20,000.

At first glance, that is a pretty significant number.  Yet, upon further reflection, it seems lilliputian and frankly incredible that all the players to have ever played in the Major Leagues don’t fill up half of Yankee Stadium.  This number is a concrete reminder of the wildly exclusive nature of playing in the Major Leagues and the sheer odds that players face to make even just one appearance.

As the number of players climbs toward 20,000, it is also worth considering the growth rate of that total.  While the world population has been growing exponentially, baseball must surely be on a more constant trajectory.  Finite numbers of teams and roster constraints simply provide a hard cap for the influx of talented ballplayers.  

In any event, getting a better idea of this growth is a worthy exercise.  How to determine growth rates though? Finding the first or last player to make an MLB debut each season seemed like a good place to start, but identifying that player seemed overly involved.  Instead, this post draws debut data from a group of players that are easily tracked and for whom it makes sense to have an MLB debut fairly consistently and very early on in the season: Rule 5 Picks.  

So, in line with these very sub-empirical standards, I utterly arbitrarily picked one player who was selected in the Rule 5 Draft, and later made at least one MLB appearance, each of the last ten seasons.  

Very simply, I wished to check the debut placement of each of these ten players and track, in what is roughly a years time between each debut, how many player debuts came in between.  This would create a general picture of whether debut numbers have been growing, slowing, or have held roughly constant over the last decade.  

Here is a table that captures these findings:

The Rule 5 players featured above have experienced varying levels of success in the majors.  Delino DeShields was a 2019 Opening Day starter.  Ryan Pressly and Marwin Gonzalez just got paid.   David Herndon and Nate Adcock haven’t been around for awhile.  Luis Perdomo and Mike Hauschild have had a harder time sticking at the games highest level, but remain very close nonetheless.

The three rightmost columns make a couple things clear (although without data for a 2008 Pick, I simply included 0’s for the two rightmost columns in David Herndon’s row).  First, the number of cumulative MLB players is in fact quickly approaching 20,000.  Second, while not exact, these players did make their debuts roughly a year apart from each other; the greatest length of days between debuts was 371 days and the fewest was 356.   The rate of MLB population growth also does appear to be roughly constant (the scatter plot below drives this point home).

The above plot does a viewer a few disservices.  For one, the debut dates are spread equidistant despite some actual variation in the distance in those points in time.  Also, it is broadly spaced enough that the year-to-year debut placements might look slightly artificially linear.  Still, the overarching relationship is clear: over the last ten years, the population of past and present MLB players has grown at a roughly constant rate. 

The average number of debuts, given these imperfect data points, in the past ten seasons has been right around 237.  In a roughly 180 day season, it is fun to know that roughly once per day, on average, a player is living out a life-long dream.  Given this rate, and simply extrapolating into the future, MLB’s 20,000th player should make his debut somewhere around midseason in 2021.  

An actual debut date is tough to pinpoint given the uneven nature of debuts over the course of a season. Debuts most often come in waves.  Waves, like with these Rule 5 players, who appear at the very beginning of any particular season.  Waves when promotions follow transactions at the Trade Deadline.  Waves when the calendar flips to September and rosters expand.

These waves and the fickle presence of injuries render any real prediction about Who’s and When’s and Where’s pretty arbitrary.  But taking a very general approach, it is fun to know that MLB’s 20,000th player is probably a member of the MiLB population currently, and that his MLB debut is coming sooner rather than later.